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    <title>Document</title>
    <script>
        let arr=[1,2,3,4,5,4,3,2,1];
        //1.数组去重
        // let result=[...new Set(arr)];
        // console.log(result);
        //2.交集
        let arr2=[4,5,6,5,6];
        // let result = [...new Set(arr)].filter(item=>{
        //     let s2=new Set(arr2);
        //     if(s2.has(item)){
        //         return true;
        //     }else{
        //         return false;
        //     }
        // })
        // let result = [...new Set(arr)].filter(item=> new Set(arr2).has(item));
        // console.log(result);
        //3.并集
        // let union=[...new Set([...arr,...arr2])];
        // console.log(union);
        //4.差集
        // let diff=[...new Set(arr)].filter(item=> !(new Set(arr2).has(item)));
        // console.log(diff);
    </script>
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